High performance microprocessor devices and the like concentrate heat in a very small space which require improved thermal cooling to maintain acceptable operating conditions. There are numerous different solutions to overcome this problem which are used in different applications such as thermally conductive pistons, micro bellows, water cooled cold plates, heat sinks, heat pipes and fans. A conventional technique used to improve thermal performance is to add finned heat sinks to increase the available surface area. Making the fins longer provides increasing thermal performance up to a point. If the fins get too long, the tips of the fins approach ambient temperature and an increase in fin length no longer improves the thermal performance. The dominate heat transfer mechanism then becomes a combination of conduction within the fin, which requires thicker or higher conductivity fins and convection from the fins to the air. Another conventional method to improve thermal performance is by improving air flow. The ultimate performance of an air cooled heat sink will be limited by available space, air flow and weight. The following patents have addressed various aspects of this problem.
U.S. Pat. No. 4,235,283 to Omkarnath teaches a thermal conduction module for cooling one or more chips via a spring loaded piston having one end in contact with the chip and the other end sliding in a hole in a massive water cooled block. Extremely good thermal performance is obtained but the system is massive and not applicable to standard semiconductor packaging techniques.
U.S. Pat. No. 5,609,202 to Anderson et. al, describes a method of improving a finned heat sink by addition of a fan within a cavity formed in the fined portion of the heat sink. This device is large and the fan tends to generate loud audible noise.
U.S. Pat. No. 5,504,924 to Ohashi et. al. utilizes a heat pipe as one of its components, but to make the heat pipe effective one end is attached to a large cooling unit which is quite cumbersome.
U.S. Pat. No. 5,335,143 to Maling et. al. describes a turbine system with spinning fins interlaced with stationary fins. This arrangement increases the mass transfer of air thereby drawing the heat from the components. The entire unit is mounted to the component or the electronic devices are mounted on the stationary fins. Relatively high speeds are required and the unit is far too large for dense, lightweight, low power applications needed for semiconductor chips.
Thus high performance cooling methods can be quite large, heavy, or consume large amounts of power or generate audible noise which are undesirable in small equipment or portable computers.